1. Field of the Invention
This invention relates to heat exchanger which is used, for example, for the recovery of exhaust heat and as an oil cooler in an internal combustion engine.
2. Description of the Related Art
A conventional heat exchanger is disclosed in Japanese Utility Model Publication No. 61(1986)-2243 in which an oil cooler includes an oil conduit through which engine oil flows. A portion of the oil conduit is mounted in a tank of the radiator, whereby the engine oil can be cooled by the cooling water. In the oil conduit within the tank there is provided an expanding and contracting body for heat exchanging which is constructed of a material having a temperature-actuated shape memory and which is called a "shape memory alloy". When the engine oil temperature rises above the transition temperature, the body will expand and increase the surface area contacting the oil conduit to increase heat transfer. By adopting the shape memory alloy, heat transfer increases at high temperature times in which increased heat transfer is required. The rate of heat transfer is decreased at low temperature times in which high heat transfer performance is not required.
In the conventional oil cooler, an outer conduit is positioned outside of an inner conduit through which a first fluid flows. A second fluid flows through an annular chamber formed between the inner conduit and the outer conduit, whereby heat exchange occurs between the first fluid and the second fluid flowing through the inner conduit and the outer conduit, respectively.
In the above conventional art, however, in order to increase the heat transfer area it is necessary to lengthen the conduit in the axial direction, and so the space provided for the heat exchanger limits the heat exchange capacity thereof. This is true for both finned and non-finned heat exchange tubes.